1. Field of the Invention
The present invention relates to a mass spectrometer, an ion mobility separator, a method of mass spectrometry and a method of ion mobility separation.
2. Discussion of the Prior Art
Radio Frequency (RF) ion guides are commonly used for confining and transporting ions. Conventionally a plurality of electrodes are provided wherein an RF voltage is applied between neighbouring electrodes so that a pseudo-potential well or valley is produced. The pseudo-potential well can be arranged to radially confine ions and may be used to efficiently transport ions by acting as an ion guide.
The RF ion guide is capable of functioning efficiently as an ion guide even at relatively high pressures wherein ions are likely to undergo frequent collisions with residual gas molecules. However, although the collisions with gas molecules may cause the ions to scatter and lose energy, the pseudo-potential well generated by the RF ion guide acts to radially confine the ions within the ion guide. RF ion guides therefore have an advantage over guide wire types of ion guides wherein a DC voltage is applied to a central wire running down the centre of a conducting tube. In such arrangements ions are held in orbit around the central guide wire and if ions undergo many collisions with gas molecules then they will tend to lose energy and will eventually collapse into the central guide wire and hence be lost. It is known to use RF ion guides to transport ions through vacuum chambers held at intermediate pressures (e.g. 0.001-10 mbar). For example, the ion guide may be provided to transmit ions from an atmospheric pressure ion source to a mass analyser in a chamber maintained at a relatively low pressure.
When ions collide with gas molecules they may get scattered and lose kinetic energy. If the ions undergo a large number of collisions, e.g. more than 100 collisions, then the ions will substantially lose all their forward kinetic energy. The ions will therefore possess a mean energy which is substantially equal to that of the surrounding gas molecules. The ions will therefore appear to move randomly within the gas due to continuing random collisions with gas molecules. Accordingly, under some operating conditions, ions being transported through an RF ion guide maintained at an intermediate gas pressure can lose substantially all their forward motion and may remain within the ion guide for a relatively long period of time.
In practice, ions may still continue to move forwards for other reasons. It is normally assumed that ions may continue to move forwards due to the bulk movement of gas forcing the ions through the ion guide. Space charge effects caused by the continual ingress of ions into the ion guide and hence the electrostatic repulsion from ions arriving from behind may also effectively push the ions through the ion guide. However, without these influences the ions can, in effect, come to a substantial standstill within the ion guide and hence not emerge at the exit.
A known means for driving ions through an RF ion guide at intermediate pressures is the use of a constant DC electric field. To ensure the ions emerge, or simply to reduce their transit time, an axial voltage gradient may be applied along the ion guide. For example, the ion guide may comprise a segmented multipole rod set ion guide with a DC potential maintained between successive rod segments. The axial electric field causes the ions to accelerate forwards after each collision with a gas molecule. A weak electric field, in the region of 0.1 to 1 V/cm, is adequate for pressures between 0.001 and 0.01 mbar. At higher pressures higher field strengths may be used.
In the pressure region above 0.001 mbar ions in an axial electric field will attain velocities according to their ion mobility. Ions emitted from a pulsed ion source can thus be arranged to separate according to their ion mobility. Ions from a continuous ion source may be gated into a drift region.
According to an aspect of the present invention there is provided a mass spectrometer comprising:
an ion mobility separator for separating ions according to their ion mobility, the ion mobility separator comprising a plurality of electrodes wherein in use one or more transient DC voltages or one or more transient DC voltage waveforms are progressively applied to the electrodes so that at least some ions having a first ion mobility are separated from other ions having a second different ion mobility.
According to a preferred embodiment a repeating pattern of electrical potentials are superimposed along the length of an ion mobility separator so as to form a periodic waveform. The waveform is caused to travel along the ion mobility separator in the direction in which it is required to move the ions and at the velocity at which it is required to move the ions.
The ion mobility separator may comprise an AC or RF ion guide such as a multipole rod set or a stacked ring set. The ion guide is preferably segmented in the axial direction so that independent transient DC potentials can be applied to each segment. The transient DC potentials are preferably superimposed on top of an AC or RF voltage which acts to radially confine ions and/or any constant DC offset voltage. The transient DC potentials generate a travelling wave which moves in the axial direction.
At any instant in time a voltage gradient is generated between segments which acts to push or pull ions in a certain direction. As the ions move in the required direction so does the voltage gradient. The individual DC voltages on each of the segments may be programmed to create a required waveform. The individual DC voltages on each of the segments may also be programmed to change in synchronism so that the DC potential waveform is maintained but is translated in the direction in which it is required to move the ions.
The one or more transient DC voltages or one or more transient DC voltage waveforms is preferably such that at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the ions having the first ion mobility are substantially moved along the ion mobility separator by the one or more transient DC voltages or the one or more transient DC voltage waveforms as the one or more transient DC voltages or the one or more transient DC voltage waveforms are progressively applied to the electrodes.
The one or more transient DC voltages or the one or more transient DC voltage waveforms are preferably such that at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the ions having the second ion mobility are moved along the ion mobility separator by the applied DC voltage to a lesser degree than the ions having the first ion mobility as the one or more transient DC voltages or the one or more transient DC voltage waveforms are progressively applied to the electrodes.
The one or more transient DC voltages or the one or more transient DC voltage waveforms are preferably such that at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the ions having the first ion mobility are moved along the ion mobility separator with a higher velocity than the ions having the second ion mobility.
According to another aspect of the present invention there is provided a mass spectrometer comprising:
an ion mobility separator for separating ions according to their ion mobility, the ion mobility separator comprising a plurality of electrodes wherein in use one or more transient DC voltages or one or more transient DC voltage waveforms are progressively applied to the electrodes so that ions are moved towards a region of the ion mobility separator wherein at least one electrode has a potential such that at least some ions having a first ion mobility will pass across the potential whereas other ions having a second different ion mobility will not pass across the potential.
The one or more transient DC voltages or the one or more transient DC voltage waveforms are preferably such that at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the ions having the first ion mobility pass across the potential. The one or more transient DC voltages or the one or more transient DC voltage waveforms are such that at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the ions having the second ion mobility will not pass across the potential. The at least one electrode is preferably provided with a voltage such that a potential hill or valley is provided.
The one or more transient DC voltages or the one or more transient DC voltage waveforms are preferably such that at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the ions having the first ion mobility exit the ion mobility separator substantially before ions having the second ion mobility. The one or more transient DC voltages or the one or more transient DC voltage waveforms are preferably such that at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the ions having the second ion mobility exit the ion mobility separator substantially after ions having the first ion mobility.
A majority of the ions having the first ion mobility preferably exit the ion mobility separator a time t before a majority of the ions having the second ion mobility exit the ion mobility separator, wherein t falls within a range selected from the group consisting of: (i)  less than 1 xcexcs; (ii) 1-10 xcexcs; (iii) 10-50 xcexcs; (iv) 50-100 xcexcs; (v) 100-200 xcexcs; (vi) 200-300 xcexcs; (vii) 300-400 xcexcs; (viii) 400-500 xcexcs; (ix) 500-600 xcexcs; (x) 600-700 xcexcs; (xi) 700-800 xcexcs; (xii) 800-900 xcexcs; (xiii) 900-1000 xcexcs; (xiv) 1.0-1.1 ms (xv) 1.1-1.2 ms; (xvi) 1.2-1.3 ms; (xvii) 1.3-1.4 ms; (xviii) 1.4-1.5 ms; (xix) 1.5-1.6 ms; (xx) 1.6-1.7 ms; (xxi) 1.7-1.8 ms; (xxii) 1.8-1.9 ms; (xxiii) 1.9-2.0 ms; (xxiv) 2.0-2.5 ms; (xxv) 2.5-3.0 ms; (xxvi) 3.0-3.5 ms; (xxvii) 3.5-4.0 ms; (xxviii) 4.0-4.5 ms; (xxix) 4.5-5.0 ms; (xxx) 5-10 ms; (xxxi) 10-15 ms; (xxxii) 15-20 ms; (xxxiii) 20-25 ms; and (xxxiv) 25-30 ms.
According to another aspect of the present invention there is provided a mass spectrometer comprising:
an ion mobility separator for separating ions according to their ion mobility, the ion mobility separator comprising a plurality of electrodes wherein in use one or more transient DC voltages or one or more transient DC voltage waveforms are progressively applied to the electrodes so that:
(i) ions are moved towards a region of the ion mobility separator wherein at least one electrode has a first potential such that at least some ions having first and second different ion mobilities will pass across the first potential whereas other ions having a third different ion mobility will not pass across the first potential; and then
(ii) ions having the first and second ion mobilities are moved towards a region of the ion mobility separator wherein at least one electrode has a second potential such that at least some ions having the first ion mobility will pass across the second potential whereas other ions having the second different ion mobility will not pass across the second potential.
The one or more transient DC voltages or the one or more transient DC voltage waveforms and the first potential are preferably such that at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the ions having the first ion mobility pass across the first potential. The one or more transient DC voltages or the one or more transient DC voltage waveforms and the first potential are preferably such that at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the ions having the second ion mobility pass across the first potential. The one or more transient DC voltages or the one or more transient DC voltage waveforms and the first potential are preferably such that at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the ions having the third ion mobility do not pass across the first potential.
The one or more transient DC voltages or the one or more transient DC voltage waveforms and the second potential are preferably such that at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the ions having the first ion mobility pass across the second potential. The one or more transient DC voltages or the one or more transient DC voltage waveforms and the second potential are preferably such that at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the ions having the second ion mobility do not pass across the second potential.
The one or more transient DC voltages or the one or more transient DC voltage waveforms are preferably such that at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the ions having the second ion mobility exit the ion mobility separator substantially before ions having the first and third ion mobilities. The one or more transient DC voltages or the one or more transient DC voltage waveforms are preferably such that at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the ions having the first and third ion mobilities exit the ion mobility separator substantially after ions having the second ion mobility.
A majority of the ions having the second ion mobility preferably exit the ion mobility separator a time t before a majority of the ions having the first and third ion mobilities exit the ion mobility separator, wherein t falls within a range selected from the group consisting of: (i)  less than 1 xcexcs; (ii) 1-10 xcexcs; (iii) 10-50 xcexcs; (iv) 50-100 xcexcs; (v) 100-200 xcexcs; (vi) 200-300 xcexcs; (vii) 300-400 xcexcs; (viii) 400-500 xcexcs; (ix) 500-600 xcexcs; (x) 600-700 xcexcs; (xi) 700-800 xcexcus; (xii) 800-900 xcexcs; (xiii) 900-1000 xcexcs; (xiv) 1.0-1.1 ms (xv) 1.1-1.2 ms; (xvi) 1.2-1.3 ms; (xvii) 1.3-1.4 ms; (xviii) 1.4-1.5 ms; (xix) 1.5-1.6 ms; (xx) 1.6-1.7 ms; (xxi) 1.7-1.8 ms; (xxii) 1.8-1.9 ms; (xxiii) 1.9-2.0 ms; (xxiv) 2.0-2.5 ms; (xxv) 2.5-3.0 ms; (xxvi) 3.0-3.5 ms; (xxvii) 3.5-4.0 ms; (xxviii) 4.0-4.5 ms; (xxix) 4.5-5.0 ms; (xxx) 5-10 ms; (xxxi) 10-15 ms; (xxxii) 15-20 ms; (xxxiii) 20-25 ms; and (xxxiv) 25-30 ms.
The one or more transient DC voltages may create: (i) a potential hill or barrier; (ii) a potential well; (iii) a combination of a potential hill or barrier and a potential well; (iv) multiple potential hills or barriers; (v) multiple potential wells; or (vi) a combination of multiple potential hills or barriers and multiple potential wells.
The one or more transient DC voltage waveforms preferably comprise a repeating waveform such as a square wave.
The one or more transient DC voltage waveforms preferably create a plurality of potential peaks or wells separated by intermediate regions. The DC voltage gradient in the intermediate regions is preferably nonzero and may be either positive or negative. The DC voltage gradient in the intermediate regions may be linear or non-linear. For example, the DC voltage gradient in the intermediate regions may increase or decrease exponentially.
The amplitude of the potential peaks or wells may remain substantially constant or the amplitude of the potential peaks or wells may become progressively larger or smaller. The amplitude of the potential peaks or wells may increase or decrease either linearly or non-linearly.
In use an axial DC voltage gradient is preferably maintained along at least a portion of the length of the ion mobility separator and wherein the axial voltage gradient varies with time.
The ion mobility separator may comprise a first electrode held at a first reference potential, a second electrode held at a second reference potential, and a third electrode held at a third reference potential, wherein: at a first time t1 a first DC voltage is supplied to the first electrode so that the first electrode is held at a first potential above or below the first reference potential; at a second later time t2 a second DC voltage is supplied to the second electrode so that the second electrode is held at a second potential above or below the second reference potential; and at a third later time t3 a third DC voltage is supplied to the third electrode so that the third electrode is held at a third potential above or below the third reference potential.
Preferably, at the first time t1 the second electrode is at the second reference potential and the third electrode is at the third reference potential; at the second time t2 the first electrode is at the first potential and the third electrode is at the third reference potential; and at the third time t3 the first electrode is at the first potential and the second electrode is at the second potential.
Alternatively, at the first time t1 the second electrode is at the second reference potential and the third electrode is at the third reference potential; at the second time t2 the first electrode is no longer supplied with the first DC voltage so that the first electrode is returned to the first reference potential and the third electrode is at the third reference potential; and at the third time t3 the first electrode is at the first reference potential the second electrode is no longer supplied with the second DC voltage so that the second electrode is returned to the second reference potential.
The first, second and third reference potentials are preferably substantially the same. Preferably, the first, second and third DC voltages are substantially the same. Preferably, the first, second and third potentials are substantially the same.
The ion mobility separator may comprise 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or  greater than 30 segments, wherein each segment comprises 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or  greater than 30 electrodes and wherein the electrodes in a segment are maintained at substantially the same DC potential. Preferably, a plurality of segments are maintained at substantially the same DC potential. Preferably, each segment is maintained at substantially the same DC potential as the subsequent nth segment wherein n is 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or  greater than 30.
Ions are preferably confined radially within the ion mobility separator by an AC or RF electric field. Ions are preferably radially confined within the ion mobility separator in a pseudo-potential well and are moved axially by a real potential barrier or well.
In use one or more additional AC or RF voltage waveforms may be applied to at least some of the electrodes so that ions are urged along at least a portion of the length of the ion mobility separator. Such AC or RF voltage waveforms are additional to the AC or RF voltages which radially confine ions within the ion mobility separator.
The transit time of ions through the ion mobility separator is preferably selected from the group consisting of: (i) less than or equal to 20 ms; (ii) less than or equal to 10 ms; (iii) less than or equal to 5 ms; (iv) less than or equal to 1 ms; and (v) less than or equal to 0.5 ms.
The ion mobility separator may be maintained in use at a pressure selected from the group consisting of: (i) greater than or equal to 0.0001 mbar; (ii) greater than or equal to 0.0005 mbar; (iii) greater than or equal to 0.001 mbar; (iv) greater than or equal to 0.005 mbar; (v) greater than or equal to 0.01 mbar; (vi) greater than or equal to 0.05 mbar; (vii) greater than or equal to 0.1 mbar; (viii) greater than or equal to 0.5 mbar; (ix) greater than or equal to 1 mbar; (x) greater than or equal to 5 mbar; and (xi) greater than or equal to 10 mbar. Preferably, the ion mobility separator is maintained in use at a pressure selected from the group consisting of: (i) less than or equal to 10 mbar; (ii) less than or equal to 5 mbar; (iii) less than or equal to 1 mbar; (iv) less than or equal to 0.5 mbar; (v) less than or equal to 0.1 mbar; (vi) less than or equal to 0.05 mbar; (vii) less than or equal to 0.01 mbar; (viii) less than or equal to 0.005 mbar; (ix) less than or equal to 0.001 mbar; (x) less than or equal to 0.0005 mbar; and (xi) less than or equal to 0.0001 mbar. Preferably, the ion mobility separator is maintained, in use, at a pressure selected from the group consisting of: (i) between 0.0001 and 10 mbar; (ii) between 0.0001 and 1 mbar; (iii) between 0.0001 and 0.1 mbar; (iv) between 0.0001 and 0.01 mbar; (v) between 0.0001 and 0.001 mbar; (vi) between 0.001 and 10 mbar; (vii) between 0.001 and 1 mbar; (viii) between 0.001 and 0.1 mbar; (ix) between 0.001 and 0.01 mbar; (x) between 0.01 and 10 mbar; (xi) between 0.01 and 1 mbar; (xii) between 0.01 and 0.1 mbar; (xiii) between 0.1 and 10 mbar; (xiv) between 0.1 and 1 mbar; and (xv) between 1 and 10 mbar.
The ion mobility separator is preferably maintained, in use, at a pressure such that a viscous drag is imposed upon ions passing through the ion mobility separator.
In use the one or more transient DC voltages or the one or more transient DC voltage waveforms are preferably initially provided at a first axial position and are then subsequently provided at second, then third different axial positions along the ion mobility separator.
The one or more transient DC voltages or the one or more transient DC voltage waveforms preferably move from one end of the ion mobility separator to another end of the ion mobility separator so that at least some ions are urged along the ion mobility separator.
The one or more transient DC voltages or the one or more transient DC voltage waveforms preferably have at least 2, 3, 4, 5, 6, 7, 8, 9 or 10 different amplitudes.
The amplitude of the one or more transient DC voltages or the one or more transient DC voltage waveforms may remain substantially constant with time or alternatively the amplitude of the one or more transient DC voltages or the one or more transient DC voltage waveforms may vary with time. For example, the amplitude of the one or more transient DC voltages or the one or more transient DC voltage waveforms either: (i) increases with time; (ii) increases then decreases with time; (iii) decreases with time; or (iv) decreases then increases with time.
The ion mobility separator may comprise an upstream entrance region, a downstream exit region and an intermediate region, wherein: in the entrance region the amplitude of the one or more transient DC voltages or the one or more transient DC voltage waveforms has a first amplitude; in the intermediate region the amplitude of the one or more transient DC voltages or the one or more transient DC voltage waveforms has a second amplitude; and in the exit region the amplitude of the one or more transient DC voltages or the one or more transient DC voltage waveforms has a third amplitude.
The entrance and/or exit region preferably comprise a proportion of the total axial length of the ion mobility separator selected from the group consisting of: (i)  less than 5%; (ii) 5-10%; (iii) 10-15%; (iv) 15-20%; (v) 20-25%; (vi) 25-30%; (vii) 30-35%; (viii) 35-40%; and (ix) 40-45%.
The first and/or third amplitudes are preferably substantially zero and the second amplitude is substantially non-zero. Preferably, the second amplitude is larger than the first amplitude and/or the second amplitude is larger than the third amplitude.
The one or more transient DC voltages or the one or more transient DC voltage waveforms preferably pass in use along the ion mobility separator with a first velocity. Preferably, the first velocity: (i) remains substantially constant; (ii) varies; (iii) increases; (iv) increases then decreases; (v) decreases; (vi) decreases then increases; (vii) reduces to substantially zero; (viii) reverses direction; or (ix) reduces to substantially zero and then reverses direction.
The one or more transient DC voltages or the one or more transient DC voltage waveforms preferably cause some ions within the ion mobility separator to pass along the ion mobility separator with a second different velocity. Preferably, the one or more transient DC voltages or the one or more transient DC voltage waveforms causes some ions within the ion mobility separator to pass along the ion mobility separator with a third different velocity. Preferably, the one or more transient DC voltages or the one or more transient DC voltage waveforms causes some ions within the ion mobility separator to pass along the ion mobility separator with a fourth different velocity. Preferably, the one or more transient DC voltages or the one or more transient DC voltage waveforms causes some ions within the ion mobility separator to pass along the ion mobility separator with a fifth different velocity.
The difference between the first velocity and the second and/or the third and/or the fourth and/or the fifth velocities is preferably selected from the group consisting of: (i) less than or equal to 50 m/s; (ii) less than or equal to 40 m/s; (iii) less than or equal to 30 m/s; (iv) less than or equal to 20 m/s; (v) less than or equal to 10 m/s; (vi) less than or equal to 5 m/s; and (vii) less than or equal to 1 m/s;
The first velocity is preferably selected from the group consisting of: (i) 10-250 m/s; (ii) 250-500 m/s; (iii) 500-750 m/s; (iv) 750-1000 m/s; (v) 1000-1250 m/s; (vi) 1250-1500 m/s; (vii) 1500-1750 m/s; (viii) 1750-2000 m/s; (ix) 2000-2250 m/s; (x) 2250-2500 m/s; (xi) 2500-2750 m/s; and (xii) 2750-3000 m/s. The second and/or the third and/or the fourth and/or the fifth different velocity is preferably selected from the group consisting of: (i) 10-250 m/s; (ii) 250-500 m/s; (iii) 500-750 m/s; (iv) 750-1000 m/s; (v) 1000-1250 m/s; (vi) 1250-1500 m/s; (vii) 1500-1750 m/s; (viii) 1750-2000 m/s; (ix) 2000-2250 m/s; (x) 2250-2500 m/s; (xi) 2500-2750 m/s; and(xii) 2750-3000 m/s.
The one or more transient DC voltages or the one or more transient DC voltage waveforms preferably has a frequency, and wherein the frequency: (i) remains substantially constant; (ii) varies; (iii) increases; (iv) increases then decreases; (v) decreases; or (vi) decreases then increases.
The one or more transient DC voltages or the one or more transient DC voltage waveforms preferably has a wavelength, and wherein the wavelength: (i) remains substantially constant; (ii) varies; (iii) increases; (iv) increases then decreases; (v) decreases; or (vi) decreases then increases.
Two or more transient DC voltages or two or more transient DC voltage waveforms may pass simultaneously along the ion mobility separator. The two or more transient DC voltages or the two or more transient DC voltage waveforms may be arranged to move: (i) in the same direction; (ii) in opposite directions; (iii) towards each other; or (iv) away from each other.
The one or more transient DC voltages or the one or more transient DC voltage waveforms may pass along the ion mobility separator and at least one substantially stationary transient DC potential voltage or voltage waveform is provided at a position along the ion mobility separator.
The one or more transient DC voltages or the one or more transient DC voltage waveforms are preferably repeatedly generated and passed in use along the ion mobility separator, and wherein the frequency of generating the one or more transient DC voltages or the one or more transient DC voltage waveforms: (i) remains substantially constant; (ii) varies; (iii) increases; (iv) increases then decreases; (v) decreases; or (vi) decreases then increases.
A continuous beam of ions may be received at an entrance to the ion mobility separator or packets of ions may be received at an entrance to the ion mobility separator.
Pulses of ions preferably emerge from an exit of the ion mobility separator. The mass spectrometer preferably further comprises an ion detector, the ion detector being arranged to be substantially phase locked in use with the pulses of ions emerging from the exit of the ion mobility separator. The mass spectrometer also preferably further comprises a Time of Flight mass analyser comprising an electrode for injecting ions into a drift region, the electrode being arranged to be energised in use in a substantially synchronised manner with the pulses of ions emerging from the exit of the ion mobility separator.
The ion mobility separator is preferably selected from the group consisting of: (i) an ion funnel comprising a plurality of electrodes having apertures therein through which ions are transmitted, wherein the diameter of the apertures becomes progressively smaller or larger; (ii) an ion tunnel comprising a plurality of electrodes having apertures therein through which ions are transmitted, wherein the diameter of the apertures remains substantially constant; and (iii) a stack of plate, ring or wire loop electrodes.
The ion mobility separator preferably comprises a plurality of electrodes, each electrode having an aperture through which ions are transmitted in use. Each electrode may have a substantially circular aperture. Each electrode may have a single aperture through which ions are transmitted in use.
The diameter of the apertures of at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the electrodes forming the ion mobility separator is preferably selected from the group consisting of: (i) less than or equal to 10 mm; (ii) less than or equal to 9 mm; (iii) less than or equal to 8 mm; (iv) less than or equal to 7 mm; (v) less than or equal to 6 mm; (vi) less than or equal to 5 mm; (vii) less than or equal to 4 mm; (viii) less than or equal to 3 mm; (ix) less than or equal to 2 mm; and (x) less than or equal to 1 mm.
At least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the electrodes forming the ion mobility separator preferably have apertures which are substantially the same size or area.
According to a less preferred embodiment the ion mobility separator may comprise a segmented rod set.
The ion mobility separator preferably consists of: (i) 10-20 electrodes; (ii) 20-30 electrodes; (iii) 30-40 electrodes; (iv) 40-50 electrodes; (v) 50-60 electrodes; (vi) 60-70 electrodes; (vii) 70-80 electrodes; (viii) 80-90 electrodes; (ix) 90-100 electrodes; (x) 100-110 electrodes; (xi) 110-120 electrodes; (xii) 120-130 electrodes; (xiii) 130-140 electrodes; (xiv) 140-150 electrodes; or (xv) more than 150 electrodes.
The thickness of at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the electrodes is preferably selected from the group consisting of: (i) less than or equal to 3 mm; (ii) less than or equal to 2.5 mm; (iii) less than or equal to 2.0 mm; (iv) less than or equal to 1.5 mm; (v) less than or equal to 1.0 mm; and (vi) less than or equal to 0.5 mm.
The ion mobility separator preferably has a length selected from the group consisting of: (i) less than 5 cm; (ii) 5-10 cm; (iii) 10-15 cm; (iv) 15-20 cm; (v) 20-25 cm; (vi) 25-30 cm; and (vii) greater than 30 cm.
At least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95% of the electrodes are preferably connected to both a DC and an AC or RF voltage supply. According to the preferred embodiment axially adjacent electrodes are supplied with AC or RF voltages having a phase difference of 180xc2x0.
The mass spectrometer may comprise an ion source selected from the group consisting of: (i) Electrospray (xe2x80x9cESIxe2x80x9d) ion source; (ii) Atmospheric Pressure Chemical Ionisation (xe2x80x9cAPCIxe2x80x9d) ion source; (iii) Atmospheric Pressure Photo Ionisation (xe2x80x9cAPPIxe2x80x9d) ion source; (iv) Matrix Assisted Laser Desorption Ionisation (xe2x80x9cMALDIxe2x80x9d) ion source; (v) Laser Desorption Ionisation (xe2x80x9cLDIxe2x80x9d) ion source; (vi) Inductively Coupled Plasma (xe2x80x9cICPxe2x80x9d) ion source; (vii) Electron Impact (xe2x80x9cEI) ion source; (viii) Chemical Ionisation (xe2x80x9cCIxe2x80x9d) ion source; (ix) a Fast Atom Bombardment (xe2x80x9cFABxe2x80x9d) ion source; and (x) a Liquid Secondary Ions Mass Spectrometry (xe2x80x9cLSIMSxe2x80x9d) ion source. The ion source may be either a continuous or a pulsed ion source.
According to another aspect of the present invention, there is provided an ion mobility separator for separating ions according to their ion mobility, the ion mobility separator comprising a plurality of electrodes wherein in use one or more transient DC voltages or one or more transient DC voltage waveforms are progressively applied to the electrodes so that at least some ions having a first ion mobility are separated from other ions having a second different ion mobility.
According to another aspect of the present invention, there is provided an ion mobility separator for separating ions according to their ion mobility, the ion mobility separator comprising a plurality of electrodes wherein in use one or more transient DC voltages or one or more transient DC voltage waveforms are progressively applied to the electrodes so that ions are moved towards a region of the ion mobility separator wherein at least one electrode has a potential such that at least some ions having a first ion mobility will pass across the potential whereas other ions having a second different ion mobility will not pass across the potential.
According to another aspect of the present invention, there is provided an ion mobility separator for separating ions according to their ion mobility, the ion mobility separator comprising a plurality of electrodes wherein in use one or more transient DC voltages or one or more transient DC voltage waveforms are progressively applied to the electrodes so that:
(i) ions are moved towards a region of the ion mobility separator wherein at least one electrode has a first potential such that at least some ions having first and second different ion mobilities will pass across the first potential whereas other ions having a third different ion mobility will not pass across the first potential; and then
(ii) ions having the first and second ion mobilities are moved towards a region of the ion mobility separator wherein at least one electrode has a second potential such that at least some ions having the first ion mobility will pass across the second potential whereas other ions having the second different ion mobility will not pass across the second potential.
According to another aspect of the present invention, there is provided a method of mass spectrometry comprising:
receiving ions in an ion mobility separator comprising a plurality of electrodes; and
progressively applying to the electrodes one or more transient DC voltages or one or more transient DC voltage waveforms so that at least some ions having a first ion mobility are separated from other ions having a second different ion mobility.
According to another aspect of the present invention, there is provided a method of mass spectrometry comprising:
receiving ions in an ion mobility separator comprising a plurality of electrodes; and
progressively applying to the electrodes one or more transient DC voltages or one or more transient DC voltage waveforms so that ions are moved towards a region of the ion mobility separator wherein at least one electrode has a potential such that at least some ions having a first ion mobility will pass across the potential whereas other ions having a second different ion mobility will not pass across the potential.
According to another aspect of the present invention, there is provided a method of mass spectrometry comprising:
receiving ions in an ion mobility separator comprising a plurality of electrodes;
progressively applying to the electrodes one or more transient DC voltages or one or more transient DC voltage waveforms so that ions are moved towards a region of the ion mobility separator wherein at least one electrode has a first potential such that at least some ions having a first and second different ion mobilities will pass across the first potential whereas other ions having a third different ion mobility will not pass across the first potential; and then
progressively applying to the electrodes one or more transient DC voltages or one or more transient DC voltage waveforms so that ions having the first and second ion mobilities are moved towards a region of the ion mobility separator wherein at least one electrode has a second potential such that at least some ions having the first ion mobility will pass across the second potential whereas other ions having the second different ion mobility will not pass across the second potential.
According to another aspect of the present invention, there is provided a method of ion mobility separation comprising:
receiving ions in an ion mobility separator comprising a plurality of electrodes; and
progressively applying to the electrodes one or more transient DC voltages or one or more transient DC voltage waveforms so that at least some ions having a first ion mobility are separated from other ions having a second different ion mobility.
According to another aspect of the present invention, there is provided a method of ion mobility separation comprising:
receiving ions in an ion mobility separator comprising a plurality of electrodes; and
progressively applying to the electrodes one or more transient DC voltages or one or more transient DC voltage waveforms so that ions are moved towards a region of the ion mobility separator wherein at least one electrode has a potential such that at least some ions having a first ion mobility will pass across the potential whereas other ions having a second different ion mobility will not pass across the potential.
According to another aspect of the present invention, there is provided a method of ion mobility separation comprising:
receiving ions in an ion mobility separator comprising a plurality of electrodes;
progressively applying to the electrodes one or more transient DC voltages or one or more transient DC voltage waveforms so that ions are moved towards a region of the ion mobility separator wherein at least one electrode has a first potential such that at least some ions having a first and second different ion mobilities will pass across the first potential whereas other ions having a third different ion mobility will not pass across the first potential; and then
progressively applying to the electrodes one or more transient DC voltages or one or more transient DC voltage waveforms so that ions having the first and second ion mobilities are moved towards a region of the ion mobility separator wherein at least one electrode has a second potential such that at least some ions having the first ion mobility will pass across the second potential whereas other ions having the second different ion mobility will not pass across the second potential.
According to another aspect of the present invention, there is provided an ion mobility separator wherein ions separate within the ion mobility separator according to their ion mobility and assume different essentially static or equilibrium axial positions along the length of the ion mobility separator.
The ion mobility separator preferably comprises a plurality of electrodes and wherein one or more transient DC voltages or one or more transient DC voltage waveforms are progressively applied to the electrodes so as to urge at least some ions in a first direction and wherein a DC voltage gradient acts to urge at least some ions in a second direction, the second direction being opposed to the first direction.
The peak amplitude of the one or more transient DC voltages or the one or more transient DC voltage waveforms preferably remains substantially constant or reduces along the length of the ion mobility separator.
The DC voltage gradient preferably progressively increases along the length of the ion mobility separator.
Once ions have assumed essentially static or equilibrium axial positions along the length of the ion mobility separator at least some of the ions may then be arranged to be moved towards an exit of the ion mobility separator. At least some of the ions may be arranged to be moved towards an exit of the ion mobility separator by: (i) reducing or increasing an axial DC voltage gradient; (ii) reducing or increasing the peak amplitude of the one or more transient DC voltages or the one or more transient DC voltage waveforms; (iii) reducing or increasing the velocity of the one or more transient DC voltages or the one or more transient DC voltage waveforms; or (iv) reducing or increasing the pressure within the ion mobility separator.
According to another aspect of the present invention, there is provided a mass spectrometer comprising an ion mobility separator as described above.
According to another aspect of the present invention, there is provided a method of ion mobility separation comprising causing ions to separate within an ion mobility separator and assume different essentially static or equilibrium axial positions along the length of the ion mobility separator.
The ion mobility separator may comprise a plurality of electrodes and wherein one or more transient DC voltages or one or more transient DC voltage waveforms are progressively applied to the electrodes so as to urge at least some ions in a first direction and wherein a DC voltage gradient acts to urge at least some ions in a second direction, the second direction being opposed to the first direction.
According to another aspect of the present invention, there is provided a method of mass spectrometry comprising:
providing an ion mobility separator for separating ions according to their ion mobility, the ion mobility separator comprising a plurality of electrodes wherein in use one or more transient DC voltages or one or more transient DC voltage waveforms are progressively applied to the electrodes so that at least some ions having a first ion mobility are separated from other ions having a second different ion mobility;
separating ions according to their ion mobility in the ion mobility separator;
providing a quadrupole mass filter downstream of the ion mobility separator; and
scanning the quadrupole mass filter in a stepped manner in synchronisation with the ion mobility separator so as to onwardly transmit ions having a desired charge state.
According to another aspect of the present invention, there is provided a mass spectrometer comprising:
an ion mobility separator for separating ions according to their ion mobility, the ion mobility separator comprising a plurality of electrodes wherein in use one or more transient DC voltages or one or more transient DC voltage waveforms are progressively applied to the electrodes so that at least some ions having a first ion mobility are separated from other ions having a second different ion mobility; and
a quadrupole mass filter downstream of the ion mobility separator;
wherein the quadrupole mass filter is scanned in use in a stepped manner in synchronisation with the ion mobility separator so as to onwardly transmit ions having a desired charge state.